A novel partner for the GTP-bound forms of rho and rac.

Using the yeast two hybrid system and overlay assays we identified a putative rholrac effector, citron, which interacts with the GTP-bound forms of rho and rac1, but not with cdc42. Extensive homologies to known proteins were not observed. This 183 kDa protein contains a C6H2 zinc finger, a PH domain, and a long coiled-coil forming region including 4 leucine zippers and the rholrac binding site. We recently identified three others putative rho effectors characterized by a common rho binding motif. Citron does not share this motif and displays a distinctive protein organization, thus defining a separate class of rho partners.